This invention relates to gas turbine engines, and relates more particularly to an improved gas turbine engine and method and control therefor particularly useful as the power plant for a ground vehicle.
Recent advances in gas turbine engine technology have improved their overall efficiency and economy to such an extent that this type of power plant has become competitive in many instances with more conventional internal combustion type power plants such as Otto or Diesel cycle engines. For instance, gas turbine technology has made significant inroads as the power plant for aircraft engines. Similarly, attempts have been made to develop a gas turbine engine which would be competitive with the more conventional internal combustion engines in high-production ground vehicles such as on-the-road automobiles and heavy trucks. The gas turbine offers significant advantages of equivalent or better operational efficiency, fuel savings, and less emissions as well as being able to utilize a variety of different fuels on an economic basis. Further, the gas turbine engine in many instances offers greater overall economy over the entire operational life of a vehicle.
The inherent operational characteristics of a gas turbine engine present, however, certain problems when utilized in a ground vehicle. More specifically, a gas turbine engine generally includes a gas generator section which provides a large pressurized air flow to a combustor wherein the air flow is mixed and ignited with fuel to greatly increase the temperature of the resulting gas flow. Hot pressurized gas flow then drives one or more turbines to produce useful rotary mechanical output power. Normally one of these turbines is a portion of the gas generator section for driving the fan which provides the high volume pressurized air inlet flow. Downstream power output turbines then generate the useful mechanical power output. Conventionally, the high speed, high volume gas flow from the gas generator drives the turbines at relatively high speeds. Other inherent characteristics of such gas turbine engines relate to the thermodynamic and aerodynamic processes carried out therewithin which dictate that operational efficiency of the engine increases substantially with increasing maximum temperature of the gas flow.
These operating characteristics of a gas turbine engine present certain disadvantages in comparison to the normal operation of reciprocating or rotary piston type internal combustion engines for ground vehicles. More particularly, the internal combustion engine inherently provides a substantial amount of deceleration horsepower for the vehicle upon reducing fuel flow thereto through the drag imposed by the reciprocating portion of the engine. In contrast, the high rotational inertia of the turbines of the gas turbine engine normally do not permit such immediate, relatively high horsepower braking for a ground vehicle simply upon reducing fuel flow to the combustor of the gas turbine engine. To overcome this disadvantage, a variety of proposals have been offered in the past to increase the braking characteristics of a gas turbine engine when utilized for driving a ground vehicle. Primarily, these concepts relate to completely extinguishing the combustion process within the combustor to produce maximum dynamic braking. However, operational life of a gas turbine engine is substantially reduced by continual thermal cycling of the entire engine as created upon extinguishing the combustion process. Further, such approaches adversely affect emissions. Other concepts relating to improving the dynamic braking characteristics of a gas turbine engine revolve around the utilization of a "fixed shaft" type of gas turbine engine wherein the gas generator section and the power drive section are mechanically interconnected to drive the vehicle. While such an arrangement improves the dynamic braking, it greatly reduces the adaptability of the engine to perform various other processes for driving a ground vehicle, and due to this limited adaptability has met with limited success in use as the power source for a high-production type of ground vehicle. An example of such prior art structure is found in U.S. Pat. No. 3,237,404. The normal method for dynamic braking in gas turbine powered aircraft, thrust reversal, is of course not readily applicable to ground vehicles.
Prior arrangements for gas turbine engines for ground vehicles also have suffered from the disadvantage of not providing efficient, yet highly responsive acceleration in comparison to internal combustion engines. Inherently, a free turbine engine normally requires a substantially longer time in developing the maximum torque required during acceleration of the ground vehicle. Prior attempts to solve this problem have centered about methods such as operating the gas generator at a constant, maximum speed, or other techniques which are equally inefficient in utilization of fuel. Overall, prior gas turbine engines for ground vehicles normally have suffered from a reduced operational efficiency in attempting to improve the acceleration or deceleration characteristics of the engine, and or resulted in reduced efficiency by substantially varying the turbine inlet temperature of the gas turbine engine which is a primary factor in the fuel consumption of the engine. Further, prior art attempts have generally been deficient in providing a reliable type of control system which is effective throughout all operational modes of a gas turbine engine when operating a ground vehicle to produce safe, reliable, operating characteristics. Further, such prior art gas turbine engines have resulted in control arrangements which present a substantial change in required operator actions in comparison to driving an internal combustion powered vehicle.
Other problems related to prior art attempts to produce a gas turbine engine for ground vehicle relate to the safety and reliability of the control system in various failure modes, safe and reliable types of controls, and in the overall operational efficiency of the engine. A majority of these problems may be considered as an outgrowth of attempts to provide a gas turbine engine presenting operational characteristics duplicative of the desirable, inherent actions of an internal combustion engine.
Accordingly, it will be seen that it would be highly desirable to provide a gas turbine engine and associated controls which incorporate the desirable operational features of both a gas turbine and internal combustion engine, but while providing an economical end product of sufficiently reliable and safe design for high volume production basis for ground vehicles.
Discussions of exemplary prior art structure relating to the engine of the present invention may be found in U.S. Pat. Nos. 3,237,404 discussed above; 3,660,976; 3,899,877; 3,941,015 all of which appear to relate to schemes for transmitting motive power from the gas generator to the engine output shaft, and 3,688,605; 3,771,916 and 3,938,321 that relate to other concepts for vehicular gas turbine engines. Examples of concepts for variable nozzle engines may also be found in U.S. Pat. Nos. 3,686,860; 3,780,527 and 3,777,479. Prior art fuel governor controls in the general class of that contemplated by the present invention may be found in U.S. Pat. Nos. 3,400,535; 3,508,395; 3,568,439; 3,712,055; 3,777,480 and 3,913,316, none of which incorporate reset and override features as contemplated by the present invention; and 3,521,446 which discloses a substantially more complex fuel reset feature than that of the present invention. Examples of other fuel controls less pertinent to the present invention may be found in U.S. Pat. Nos. 3,851,464 and 3,888,078. U.S. Pat. No. 3,733,815 relates to the automatic idle reset feature of the present invention while U.S. Pat. Nos. 2,976,683; 3,183,667 and 3,820,323 relate to the scheduling valve controls.